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Drugs Acting on Autonomic Nervous System - Cholinergic System and Drugs

Q: What is the mechanism by which choline is taken up by the axonal membrane?

Choline uptake occurs via a Na+ : choline cotransporter present in the axonal membrane.

92 important questions on Drugs Acting on Autonomic Nervous System - Cholinergic System and Drugs

What is the mechanism by which choline is taken up by the axonal membrane?

Choline uptake occurs via a Na+: choline cotransporter present in the axonal membrane.

How is acetylcholine (ACh) synthesized in the axoplasm?

Acetylation of choline occurs using ATP, coenzyme A, and choline acetyltransferase.

What effect does hemicholinium (HC3) have on ACh?

Hemicholinium blocks choline uptake, thereby depleting acetylcholine levels.

Where is the majority of ACh stored in cholinergic terminals?

Most ACh is stored in small synaptic vesicles in an ionic solution.

What does vesamicol inhibit in the synaptic vesicles?

Vesamicol inhibits the active transport of ACh into synaptic vesicles.

How is ACh released from nerve terminals?

Release occurs via exocytosis in small quanta contained in vesicles.

What happens when multiple quanta of ACh are released?

Synchronous release triggers postjunctional events in response to nerve AP.

What is the action of botulinum toxin on cholinergic transmission?

Botulinum toxin inhibits ACh release, causing long-lasting loss of transmission.

What conditions can localized botulinum toxin A injection treat?

It treats spastic conditions like blepharospasm and nystagmus, among others.

What is the role of esterase enzymes in ACh lifecycle?

Cholinesterase hydrolyzes ACh, allowing choline to be recycled.

How many classes of ACh receptors are recognized?

There are two classes recognized: muscarinic and nicotinic receptors.

What receptors are affected by muscarine and blocked by atropine?

Muscarinic receptors are selectively stimulated by muscarine and blocked by atropine.

Which receptors are primarily located on cardiac tissues?

Cardiac tissues predominantly express M2 muscarinic receptors for vagal bradycardia.

What is the function of M3 muscarinic receptors in smooth muscles?

M3 receptors mediate visceral smooth muscle contraction and glandular secretions.

What is the primary action of nicotinic receptors?

Nicotinic receptors cause rapid depolarization and action potential upon activation.

What are cholinomimetic drugs designed to do?

Cholinomimetic drugs act similarly to ACh by either stimulating receptors or inhibiting enzymes.

What is the primary use of pilocarpine?

Pilocarpine is primarily used as eye drops to treat glaucoma and induce miosis.

How does neostigmine improve muscle contraction in myasthenia gravis?

Neostigmine allows ACh to accumulate and directly depolarizes the muscle endplate.

What complications can arise from incorrect injection of botulinum toxin?

Incorrect injection can lead to ptosis, dysphagia, and even respiratory paralysis.

Which drug is used as a specific antidote for anticholinergic poisoning?

Physostigmine is used as the specific antidote for anticholinergic poisoning.

How does myasthenia gravis primarily affect muscle function?

It causes weakness and easy fatigability due to reduced nicotinic receptors at muscle endplate.

How is choline taken up by the axonal membrane?

Through a Na+: choline cotransporter and acetylated by choline acetyl transferase.

What blocks choline uptake and depletes ACh?

Hemicholinium (HC3) blocks uptake, the rate limiting step in ACh synthesis.

Where is most ACh stored?

Within small synaptic vesicles in ionic solution; some is free in the cytoplasm.

What carrier is blocked by vesamicol?

Another carrier that transports ACh into synaptic vesicles is blocked by vesamicol.

How is ACh released from nerve terminals?

ACh release is in small quanta through exocytosis, triggered by nerve AP.

What does botulinum toxin do to cholinergic transmission?

It inhibits release of ACh, causing long-lasting loss of cholinergic transmission.

What are the two classes of receptors for ACh?

They are muscarinic and nicotinic receptors with different functions.

What is the primary action of muscarinic receptors?

These receptors mediate various functions like secretion, contraction, and vasodilatation.

What happens when ACh binds to muscarinic receptors?

It stimulates the release of endothelium-dependent relaxing factor (EDRF).

What are the major subtypes of muscarinic receptors?

M1, M2, and M3 are major subtypes; M4 and M5 are less common.

What is the main function of choline in the axonal membrane?

Choline is taken up and acetylated to form ACh using ATP and coenzyme A.

Which transporter is involved in the uptake of choline?

A Na+: choline cotransporter is responsible for choline uptake.

How is acetylcholine synthesized?

Acetylcholine is synthesized by acetylation through choline acetyltransferase.

What role does hemicholinium (HC3) play in ACh synthesis?

Hemicholinium blocks choline uptake, affecting ACh synthesis rate.

Where is most acetylcholine stored?

Most ACh is stored in ionic solution within small synaptic vesicles.

What effect does vesamicol have on acetylcholine transport?

Vesamicol blocks the carrier responsible for ACh transport into vesicles.

How is ACh released from nerve terminals?

ACh is released in small quanta via exocytosis.

What triggers postjunctional events in neurons?

Synchronous release of multiple quanta triggers postjunctional events after a nerve AP.

What is the effect of botulinum toxin on ACh release?

Botulinum toxin inhibits ACh release, causing long-lasting loss of cholinergic transmission.

What are the two types of botulinum toxins?

Botulinum toxin A and B are potent exotoxins causing botulism.

What is the use of localized injection of botulinum toxin?

Used to treat various spastic neurological conditions and facial wrinkles.

What side effects can occur from incorrect injection of botulinum toxin?

Side effects include ptosis, diplopia, and even respiratory paralysis.

What happens to ACh immediately after its release?

ACh is hydrolyzed by cholinesterase, and choline is recycled.

What are the two classes of cholinesterase enzymes?

Acetylcholinesterase (AChE) and Butyrylcholinesterase (BuChE).

Where is AChE located in the body?

AChE is located at all cholinergic sites to inactivate ACh instantly.

What are muscarinic receptors activated by?

Activated by muscarine and blocked by atropine.

Where are muscarinic receptors primarily located?

Located on autonomic effector cells in various organs.

What roles do muscarinic autoreceptors play?

They inhibit further ACh release from postganglionic cholinergic nerve endings.

How do blood vessels respond to muscarinic receptor activation?

Activation releases EDRF (nitric oxide), causing vasodilation.

How many subtypes of muscarinic receptors are identified?

Five subtypes: M1, M2, M3, M4, and M5.

What is the primary role of the M1 receptor?

The M1 receptor mediates gastric secretion, learning, and memory.

What effect do M2 receptors have on the heart?

M2 receptors mediate vagal bradycardia and affect conduction.

What is the function of M3 receptors?

M3 receptors mediate visceral smooth muscle contraction and glandular secretions.

What happens when cholinergic drugs stimulate nicotinic receptors?

Nicotinic receptor activation leads to rapid depolarization and action potential generation.

What distinguishes NM and NN subtypes of nicotinic receptors?

NM is at skeletal muscle endplates; NN is on ganglionic cells.

What do cholinomimetic drugs do?

They produce actions similar to acetylcholine, either directly or indirectly.

How does acetylcholine affect the heart?

It decreases the rate of diastolic depolarization, leading to bradycardia.

What effect does ACh have on cardiac conduction?

ACh can slow conduction and increase refractory period in atria.

What occurs in blood vessels after ACh release?

Blood vessels dilate, especially in areas with cholinergic innervation.

Which muscles contract due to ACh's action?

Smooth muscles contract and peristalsis increases in gastrointestinal tract.

Summarize ACh's effect on glands.

ACh increases secretion from all parasympathetically innervated glands.

What is the result of ACh activation in the eye?

Activation leads to miosis and increased outflow facility, lowering intraocular tension.

How do higher doses of ACh impact autonomic ganglia?

They stimulate both sympathetic and parasympathetic ganglia.

What types of receptors affect skeletal muscle contraction?

NM receptors at the muscle endplate mediate contraction.

What is the effect of cholinergic drugs on the CNS?

They can produce behavioral effects and may improve cognitive function.

Why are cholinergic drugs rarely clinically used?

ACh is evanescent and nonselective, causing prominent side effects.

What are cholinomimetics classified by?

They are categorized based on receptor types and action mechanisms.

What is the mechanism of action of M-cholinemimetics?

They primarily stimulate M receptors affecting various body systems.

How do M-cholinemimetics affect the eye?

Pupil diameter decreases, intraocular tension lowers, and accommodation improves.

What effects do M-cholinomimetics have on the heart?

Heart rate decreases and cardiac output is reduced due to receptor stimulation.

What actions do M-cholinomimetics have on smooth muscles?

They cause contraction in bronchi, digestive tube, urinary bladder, and other organs.

What are the indications for using M-cholinomimetics?

They treat conditions like glaucoma, urinary retention, and gastrointestinal problems.

What are contraindications for M-cholinomimetics?

They should be avoided in asthma, peptic ulcers, and bradycardia cases.

What kind of adverse reactions can M-cholinomimetics cause?

They may lead to nausea, diarrhea, sweating, and blurred vision.

What is the toxic action of muscarine?

It leads to symptoms resembling excessive cholinergic stimulation or poisoning.

What is the main antidote for muscarine poisoning?

Atropine serves as the main antidote, counteracting cholinergic effects.

What do N-cholinomimetics primarily interact with?

They act on sinocarotid receptors and affect ganglia and muscles.

What are the indications for N-cholinomimetics?

They are used in myasthenia gravis and other neuromuscular disorders.

What are common contraindications for N-cholinomimetics?

They should not be used in obstructive airway diseases or hypersensitivity.

What are the side effects of N-cholinomimetics?

They may cause muscle cramps, increased salivation, and respiratory distress.

What are the main components of cigarette smoke?

Cigarette smoke comprises tar, nicotine, carbon monoxide, and numerous chemicals.

What diseases are caused by smoking?

Smoking leads to lung cancer, chronic bronchitis, and cardiovascular diseases.

How do N-cholinomimetics help combat smoking?

They may reduce withdrawal symptoms and cravings associated with nicotine addiction.

What are anticholinesterase preparations?

They inhibit the enzyme cholinesterase, increasing acetylcholine availability.

How are anticholinesterases classified?

They are categorized into reversible and irreversible types based on their effect.

What is the mechanism of action of organophosphorus compounds?

They irreversibly bind and inhibit cholinesterase, leading to excessive acetylcholine.

What are the indications for anticholinesterase preparations?

They are used in treating myasthenia gravis and Alzheimer's disease among others.

What are the contraindications for anticholinesterase preparations?

They should not be used in patients with asthma or certain heart conditions.

What are the adverse reactions of anticholinesterase preparations?

They may cause muscle twitching, triad of symptoms, and gastrointestinal disturbances.

What is the clinical picture of organophosphorus poisoning?

Symptoms include salivation, sweating, diarrhea, and respiratory failure.

What are the antidotes for organophosphorus compounds?

Atropine and pralidoxime are used as antidotes, aiding in recovery.

The question on the page originate from the summary of the following study material:

Essentials of Medical Pharmacology | 9789350259375 | KD Tripathi

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